1. Field of Invention
This invention is related to aqueous dispersions of perfluoroolefin polymers and particularly to coatings based on polymers of tetrafluoroethylene (TFE) and tetrafluoroethylene/hexafluoropropylene (HFP), containing other film-forming materials.
2. Description of Prior Art
Aqueous dispersions of PTFE and of TFE/HFP copolymers are well known in the prior art and can be used to coat or impregnate articles. These aqueous dispersions, however, have a tendency to coagulate irreversibly when subjected to heat, freezing, agitation or upon addition of electrolytes or water soluble solvents. Some of these short-comings can be eliminated when dispersions of these polymers are prepared in organic liquids. In many cases, however, these dispersions settle quickly and are often not suitable for commercial use.
When a dispersion in organic liquid also contains, in addition to a perfluoroolefin polymer, a film-forming material, a stable dispersion results. U.S. Pat. No. 3,661,831, issued May 9, 1972, to J. C. Fang, shows such stabilized dispersions of TFE/HFP copolymers, while U.S. Pat. application, Ser. No. 361,819, filed May 18, 1973, shows the use of stabilized PTFE dispersions. In both cases the dispersions are substantially anhydrous, that is, contain less than about 1% by weight of water.
Increased awareness, however, of the environmental hazards of allowing organic solvent vapors to enter the atmosphere, the desirability of a single system that can be applied not only by the more conventional techniques of spray or roller coating but also by electrodeposition, and the economy resulting from the substitution of water for some or all of the solvents in a coating composition, are all factors mitigating in favor of aqueous dispersions.
The aqueous dispersions of this invention contain a perfluoroolefin polymer which can be a polymer of TFE or of a mixture of TFE and HFP and a film-forming material such as a polyamide acid salt or a polymeric quaternary hydroxide blended with a nitrogen-resin, can be applied by a variety of techniques, and the fused/cured films obtained have excellent release properties, high lubricity and resistance to heat and chemicals, and are good electrical insulators.